Hi J Edwards!
When you create an organization, you are automatically the administrator and the eSignature account used to create the organization is the default account. An organization's default account is used for just-in-time provisioning when new users are added. Also, based on your default account plan, your Organization features will be available to you. But, besides that, I can’t think in another scenario to must change this default account.
I suggest you to create a ticket to our Technical Support team asking it, because I didn’t find any way to change the default account directly from your DS Admin application.